my brother is thinking of getting couple,and havn't really found a good reliable one yet. also if the tank is big enough can you house females together
Yes females can be house together, but they can still bicker. Make sure the geckos are size the same if buying younger ones.
There are a lot of care sheets if you do a search on the web for it.
Here is one that looks pretty good http://www.anapsid.org/tokays.html
I would read a lot and ask any specifics from there.
BTW personally I do not feel as if a 20 gallon is big enough for a tokay (adult)
I would go as large as you can keeping 3 feet height as minimal.